2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
25 #include "ucioption.h"
27 using namespace Search;
29 ThreadsManager Threads; // Global object
31 namespace { extern "C" {
33 // start_routine() is the C function which is called when a new thread
34 // is launched. It simply calls idle_loop() of the supplied thread. The first
35 // and last thread are special. First one is the main search thread while the
36 // last one mimics a timer, they run in main_loop() and timer_loop().
39 DWORD WINAPI start_routine(LPVOID thread) {
41 void* start_routine(void* thread) {
44 Thread* th = (Thread*)thread;
46 if (th->threadID == 0)
49 else if (th->threadID == MAX_THREADS)
61 // wake_up() wakes up the thread, normally at the beginning of the search or,
62 // if "sleeping threads" is used, when there is some work to do.
64 void Thread::wake_up() {
66 lock_grab(&sleepLock);
67 cond_signal(&sleepCond);
68 lock_release(&sleepLock);
72 // cutoff_occurred() checks whether a beta cutoff has occurred in the current
73 // active split point, or in some ancestor of the split point.
75 bool Thread::cutoff_occurred() const {
77 for (SplitPoint* sp = splitPoint; sp; sp = sp->parent)
78 if (sp->is_betaCutoff)
85 // is_available_to() checks whether the thread is available to help the thread with
86 // threadID "master" at a split point. An obvious requirement is that thread must be
87 // idle. With more than two threads, this is not by itself sufficient: If the thread
88 // is the master of some active split point, it is only available as a slave to the
89 // threads which are busy searching the split point at the top of "slave"'s split
90 // point stack (the "helpful master concept" in YBWC terminology).
92 bool Thread::is_available_to(int master) const {
97 // Make a local copy to be sure doesn't become zero under our feet while
98 // testing next condition and so leading to an out of bound access.
99 int localActiveSplitPoints = activeSplitPoints;
101 // No active split points means that the thread is available as a slave for any
102 // other thread otherwise apply the "helpful master" concept if possible.
103 if ( !localActiveSplitPoints
104 || splitPoints[localActiveSplitPoints - 1].is_slave[master])
111 // read_uci_options() updates number of active threads and other parameters
112 // according to the UCI options values. It is called before to start a new search.
114 void ThreadsManager::read_uci_options() {
116 maxThreadsPerSplitPoint = Options["Max Threads per Split Point"];
117 minimumSplitDepth = Options["Min Split Depth"] * ONE_PLY;
118 useSleepingThreads = Options["Use Sleeping Threads"];
120 set_size(Options["Threads"]);
124 // set_size() changes the number of active threads and raises do_sleep flag for
125 // all the unused threads that will go immediately to sleep.
127 void ThreadsManager::set_size(int cnt) {
129 assert(cnt > 0 && cnt <= MAX_THREADS);
133 for (int i = 1; i < MAX_THREADS; i++) // Ignore main thread
134 if (i < activeThreads)
136 // Dynamically allocate pawn and material hash tables according to the
137 // number of active threads. This avoids preallocating memory for all
138 // possible threads if only few are used.
139 threads[i].pawnTable.init();
140 threads[i].materialTable.init();
142 threads[i].do_sleep = false;
145 threads[i].do_sleep = true;
149 // init() is called during startup. Initializes locks and condition variables
150 // and launches all threads sending them immediately to sleep.
152 void ThreadsManager::init() {
154 // Initialize sleep condition and lock used by thread manager
155 cond_init(&sleepCond);
156 lock_init(&threadsLock);
158 // Initialize thread's sleep conditions and split point locks
159 for (int i = 0; i <= MAX_THREADS; i++)
161 lock_init(&threads[i].sleepLock);
162 cond_init(&threads[i].sleepCond);
164 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
165 lock_init(&(threads[i].splitPoints[j].lock));
168 // Allocate main thread tables to call evaluate() also when not searching
169 threads[0].pawnTable.init();
170 threads[0].materialTable.init();
172 // Create and launch all the threads, threads will go immediately to sleep
173 for (int i = 0; i <= MAX_THREADS; i++)
175 threads[i].is_searching = false;
176 threads[i].do_sleep = (i != 0); // Avoid a race with start_thinking()
177 threads[i].threadID = i;
179 #if defined(_MSC_VER)
180 threads[i].handle = CreateThread(NULL, 0, start_routine, &threads[i], 0, NULL);
181 bool ok = (threads[i].handle != NULL);
183 bool ok = !pthread_create(&threads[i].handle, NULL, start_routine, &threads[i]);
188 std::cerr << "Failed to create thread number " << i << std::endl;
189 ::exit(EXIT_FAILURE);
195 // exit() is called to cleanly terminate the threads when the program finishes
197 void ThreadsManager::exit() {
199 for (int i = 0; i <= MAX_THREADS; i++)
201 threads[i].do_terminate = true; // Search must be already finished
202 threads[i].wake_up();
204 // Wait for thread termination
205 #if defined(_MSC_VER)
206 WaitForSingleObject(threads[i].handle, INFINITE);
207 CloseHandle(threads[i].handle);
209 pthread_join(threads[i].handle, NULL);
212 // Now we can safely destroy associated locks and wait conditions
213 lock_destroy(&threads[i].sleepLock);
214 cond_destroy(&threads[i].sleepCond);
216 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
217 lock_destroy(&(threads[i].splitPoints[j].lock));
220 lock_destroy(&threadsLock);
221 cond_destroy(&sleepCond);
225 // available_slave_exists() tries to find an idle thread which is available as
226 // a slave for the thread with threadID 'master'.
228 bool ThreadsManager::available_slave_exists(int master) const {
230 assert(master >= 0 && master < activeThreads);
232 for (int i = 0; i < activeThreads; i++)
233 if (threads[i].is_available_to(master))
240 // split_point_finished() checks if all the slave threads of a given split
241 // point have finished searching.
243 bool ThreadsManager::split_point_finished(SplitPoint* sp) const {
245 for (int i = 0; i < activeThreads; i++)
253 // split() does the actual work of distributing the work at a node between
254 // several available threads. If it does not succeed in splitting the node
255 // (because no idle threads are available, or because we have no unused split
256 // point objects), the function immediately returns. If splitting is possible, a
257 // SplitPoint object is initialized with all the data that must be copied to the
258 // helper threads and then helper threads are told that they have been assigned
259 // work. This will cause them to instantly leave their idle loops and call
260 // search(). When all threads have returned from search() then split() returns.
263 Value ThreadsManager::split(Position& pos, Stack* ss, Value alpha, Value beta,
264 Value bestValue, Depth depth, Move threatMove,
265 int moveCount, MovePicker* mp, int nodeType) {
266 assert(pos.pos_is_ok());
267 assert(bestValue > -VALUE_INFINITE);
268 assert(bestValue <= alpha);
269 assert(alpha < beta);
270 assert(beta <= VALUE_INFINITE);
271 assert(depth > DEPTH_ZERO);
272 assert(pos.thread() >= 0 && pos.thread() < activeThreads);
273 assert(activeThreads > 1);
275 int i, master = pos.thread();
276 Thread& masterThread = threads[master];
278 // If we already have too many active split points, don't split
279 if (masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
282 // Pick the next available split point from the split point stack
283 SplitPoint* sp = &masterThread.splitPoints[masterThread.activeSplitPoints];
285 // Initialize the split point
286 sp->parent = masterThread.splitPoint;
288 sp->is_betaCutoff = false;
290 sp->threatMove = threatMove;
293 sp->nodeType = nodeType;
294 sp->bestValue = bestValue;
296 sp->moveCount = moveCount;
301 for (i = 0; i < activeThreads; i++)
302 sp->is_slave[i] = false;
304 // If we are here it means we are not available
305 assert(masterThread.is_searching);
307 int workersCnt = 1; // At least the master is included
309 // Try to allocate available threads and ask them to start searching setting
310 // is_searching flag. This must be done under lock protection to avoid concurrent
311 // allocation of the same slave by another master.
312 lock_grab(&threadsLock);
314 for (i = 0; !Fake && i < activeThreads && workersCnt < maxThreadsPerSplitPoint; i++)
315 if (threads[i].is_available_to(master))
318 sp->is_slave[i] = true;
319 threads[i].splitPoint = sp;
321 // This makes the slave to exit from idle_loop()
322 threads[i].is_searching = true;
324 if (useSleepingThreads)
325 threads[i].wake_up();
328 lock_release(&threadsLock);
330 // We failed to allocate even one slave, return
331 if (!Fake && workersCnt == 1)
334 masterThread.splitPoint = sp;
335 masterThread.activeSplitPoints++;
337 // Everything is set up. The master thread enters the idle loop, from which
338 // it will instantly launch a search, because its is_searching flag is set.
339 // We pass the split point as a parameter to the idle loop, which means that
340 // the thread will return from the idle loop when all slaves have finished
341 // their work at this split point.
342 masterThread.idle_loop(sp);
344 // In helpful master concept a master can help only a sub-tree of its split
345 // point, and because here is all finished is not possible master is booked.
346 assert(!masterThread.is_searching);
348 // We have returned from the idle loop, which means that all threads are
349 // finished. Note that changing state and decreasing activeSplitPoints is done
350 // under lock protection to avoid a race with Thread::is_available_to().
351 lock_grab(&threadsLock);
353 masterThread.is_searching = true;
354 masterThread.activeSplitPoints--;
356 lock_release(&threadsLock);
358 masterThread.splitPoint = sp->parent;
359 pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
361 return sp->bestValue;
364 // Explicit template instantiations
365 template Value ThreadsManager::split<false>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
366 template Value ThreadsManager::split<true>(Position&, Stack*, Value, Value, Value, Depth, Move, int, MovePicker*, int);
369 // Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
370 // then calls do_timer_event(). If maxPly is 0 thread sleeps until is woken up.
371 extern void check_time();
373 void Thread::timer_loop() {
375 while (!do_terminate)
377 lock_grab(&sleepLock);
378 timed_wait(&sleepCond, &sleepLock, maxPly ? maxPly : INT_MAX);
379 lock_release(&sleepLock);
385 // ThreadsManager::set_timer() is used to set the timer to trigger after msec
386 // milliseconds. If msec is 0 then timer is stopped.
388 void ThreadsManager::set_timer(int msec) {
390 Thread& timer = threads[MAX_THREADS];
392 lock_grab(&timer.sleepLock);
394 cond_signal(&timer.sleepCond); // Wake up and restart the timer
395 lock_release(&timer.sleepLock);
399 // Thread::main_loop() is where the main thread is parked waiting to be started
400 // when there is a new search. Main thread will launch all the slave threads.
402 void Thread::main_loop() {
406 lock_grab(&sleepLock);
408 do_sleep = true; // Always return to sleep after a search
409 is_searching = false;
411 while (do_sleep && !do_terminate)
413 cond_signal(&Threads.sleepCond); // Wake up UI thread if needed
414 cond_wait(&sleepCond, &sleepLock);
419 lock_release(&sleepLock);
429 // ThreadsManager::start_thinking() is used by UI thread to wake up the main
430 // thread parked in main_loop() and starting a new search. If asyncMode is true
431 // then function returns immediately, otherwise caller is blocked waiting for
432 // the search to finish.
434 void ThreadsManager::start_thinking(const Position& pos, const LimitsType& limits,
435 const std::set<Move>& searchMoves, bool async) {
436 Thread& main = threads[0];
438 lock_grab(&main.sleepLock);
440 // Wait main thread has finished before to launch a new search
441 while (!main.do_sleep)
442 cond_wait(&sleepCond, &main.sleepLock);
444 // Copy input arguments to initialize the search
445 RootPosition.copy(pos, 0);
449 // Populate RootMoves with all the legal moves (default) or, if a searchMoves
450 // set is given, with the subset of legal moves to search.
451 for (MoveList<MV_LEGAL> ml(pos); !ml.end(); ++ml)
452 if (searchMoves.empty() || searchMoves.count(ml.move()))
453 RootMoves.push_back(RootMove(ml.move()));
455 // Reset signals before to start the new search
456 Signals.stopOnPonderhit = Signals.firstRootMove = false;
457 Signals.stop = Signals.failedLowAtRoot = false;
459 main.do_sleep = false;
460 cond_signal(&main.sleepCond); // Wake up main thread and start searching
463 while (!main.do_sleep)
464 cond_wait(&sleepCond, &main.sleepLock);
466 lock_release(&main.sleepLock);
470 // ThreadsManager::stop_thinking() is used by UI thread to raise a stop request
471 // and to wait for the main thread finishing the search. Needed to wait exiting
472 // and terminate the threads after a 'quit' command.
474 void ThreadsManager::stop_thinking() {
476 Thread& main = threads[0];
478 Search::Signals.stop = true;
480 lock_grab(&main.sleepLock);
482 cond_signal(&main.sleepCond); // In case is waiting for stop or ponderhit
484 while (!main.do_sleep)
485 cond_wait(&sleepCond, &main.sleepLock);
487 lock_release(&main.sleepLock);
491 // ThreadsManager::wait_for_stop_or_ponderhit() is called when the maximum depth
492 // is reached while the program is pondering. The point is to work around a wrinkle
493 // in the UCI protocol: When pondering, the engine is not allowed to give a
494 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command. We simply
495 // wait here until one of these commands (that raise StopRequest) is sent and
496 // then return, after which the bestmove and pondermove will be printed.
498 void ThreadsManager::wait_for_stop_or_ponderhit() {
500 Signals.stopOnPonderhit = true;
502 Thread& main = threads[0];
504 lock_grab(&main.sleepLock);
506 while (!Signals.stop)
507 cond_wait(&main.sleepCond, &main.sleepLock);
509 lock_release(&main.sleepLock);